FORMER Prime Minister Gordon Brown has waded into the debate on Sottish independence, claiming people north of the border would lose their pensions if they went it alone from September.

They haven't answered the basic problem - you have paid into your pension, into the UK Exchequer all your lives, you've paid your national insurance, you've paid your taxes so that you have a right to a pension

Gordon Brown

In a rare intervention into national politics, Mr Brown accused the Scottish National Party (SNP) of not addressing the "basic problem" of how pensions would be paid post-independence.

Mr Brown, who was born in Renfrewshire, Scotland, and served as Prime Minister of the UK from 2007 until 2010, said Scottish pensioners had a good deal from the union, receiving around £200 more on average each year in benefits than their English counterparts.

Addressing an audience of pensioners at an event in Lochgelly, Fife, to launch the campaign group Keep our British Pensions, Mr Brown said: "The SNP know that they have got a problem... the rising demand for pensions, set against the money that they have, means there is greater volatility in social security spending."

"They haven't answered the basic problem - you have paid into your pension, into the UK Exchequer all your lives, you've paid your national insurance, you've paid your taxes so that you have a right to a pension.

"You are expecting, quite rightly, that you will get a British pension - but if there is independence, the British pension stops, the national insurance fund that you're paying into is broken up.

"There will be a separate Scottish national insurance fund, and the rest of the UK will have the lion's share."

The Kirkcaldy and Cowdenbeath MP cited pensioners' credit, the winter fuel allowance and free television licences as areas in which Scottish pensioners benefit by being part of the UK.

He said: "Why does that happen? It happens because we pool all of our resources as part of the United Kingdom.

"We pay our national insurance and we pay our taxes so that we can pay for our pensions later.

"We have more needs (in Scotland) and more pensioners, therefore we get more."

Mr Brown argued that the SNP's estimates for oil revenues - which would help fund pensions under independence - were at odds with private documents leaked to the media.

"They didn't expect to get £6.9billion from oil, they only expect to get £4billion...far from having all these billions of resources, the SNP are exaggerating all the time.

"That difference of over two billion is the equivalent of half the amount of money spent on everybody's pension in Scotland.

It is the third time in a week the SNP's independence campaign has come under attack from senior political figures.

Last week the Conservative Chancellor George Osborne, Labour's Shadow Chancellor Ed Balls and the Lib Dem Chief Secretary to the Treasury Danny Alexander all ruled out Britain entering into a currency union with an independent Scotland.

On Sunday, European Commission President Jose Manuel Barroso said it would "extremely difficult" for Scotland to join the EU, saying countries such as Spain would likely veto any application.

The SNP described Mr Brown's comments as "scaremongering".

Deputy First Minister and SNP depute leader Nicola Sturgeon said: "The last person anyone in Scotland will take lessons from when it comes to pensions is Gordon Brown - the man who destroyed final-salary pension schemes with his £100 billion raid, and insulted our older folk with a miserly 75p increase in the state pension.

"Mr Brown's track record means that he lacks all credibility on this subject, so it is little wonder that his speech bears little relationship with reality.

"The Scottish Government has set out clearly and unambiguously that people will continue to receive the pension entitlements they have built up - and any attempt to insinuate otherwise is grossly irresponsible.

"Social protection costs represent a lower share of tax revenues in Scotland than for the UK as a whole - meaning pensions are more affordable for Scotland - and academic surveys and polls consistently show that people want decisions on pensions and welfare to be made in the Scottish Parliament rather than by Westminster.

Ms Sturgeon said National Institute of Economic Research showed that pensions in Scotland would be six per cent to eight per cent cheaper than in the rest of the UK.

"Where Westminster has decimated pension schemes and is rushing ahead an accelerated timetable that will see the retirement age rise rapidly, a Yes vote in September will ensure we have a pensions system that is right for Scotland," she said.